1. Field of the Invention
The invention relates to devices for presenting visual displays of input signals such as the displays shown on cathode ray tubes (CRT's). More particularly, the present invention relates to display devices utilizing liquid crystals and electrode and scanning arrangements therefor.
The invention contemplates utilization of liquid crystal materials in which the propagation or characteristics of light incidence thereon can be altered by inducing an electric or magnetic field in the liquid crystal material. Such liquid crystal materials include, but are not limited to, nematic liquid crystal materials possessing dynamic or quiescent scattering, or twisted field-effect electro-optical properties, and the mixtures of these nematic liquid crystal materials with cholesteric liquid crystal materials.
In a dynamic scattering liquid crystal material, light is transmitted substantially unaffected through the material in the absence of an electric field across the liquid material. When an electric field of sufficient magnitude is induced in the liquid crystal material, light incident upon the material is optically scattered and transmission of light through the material is substantially prevented.
A quiescent scattering liquid crystal material possesses field effective electro-optical properties which are the converse of those of the dynamic scattering liquid crystal. Thus, in the absence of an electric field, the quiescent scattering liquid crystal material scatters incident light, while an electric field induced in the quiescent liquid crystal material causes it to transmit incident light therethrough.
In a twisted nematic liquid crystal material, layers of molecules at opposed surfaces of the material can be caused to be aligned at an angle with each other in the absence of a field. The molecules between the opposed surfaces have varying angular alignments with the result that the molecular orientation through the material from one surface to the other is helical of "twisted". The plane of polarization of plane polarized light is rotated by the angle formed by the opposed surface molecules as the light passes through the liquid crystal material in the absence of a field. The application of an electric field to the material destroys the twisted alignment of the molecules with the result that the material transmits incident plane polarized light therethrough without substantial rotation of the plane of polarization.
Cathode-ray tube oscilloscopes are used to produce a luminuous plot on a fluorescent screen which is the graphical representation of an electric signal being used as the input. Motion of a focused spot leaves a visible trace on the phosphor on the viewing screen of the tube. The primary advantage of cathode-ray oscillcscopes over other forms of plotting devices is its speed of response. Commercially available instruments can display frequencies as high as 2 GHz.
2. Prior Art
Liquid crystal materials of the types referred to above, as well as others, are well known in the prior art. See, for example, G. Heilmeier, "Liquid-Crystal Display Device", Scientific American, April, 1970, pp. 100-106; G. Heilmeier, L. Zanoni & L. Barton, "Dynamic Scattering: A New Electro-optic Effect in Certain Classes of Nematic Liquid Crystals", Proceedings of the IEEE, Vol. 56, No. 7, July 1968, pp. 1162-1171; and U.S. Pat. No. 3,918,796, issued on Nov. 11, 1975, to Fergason.
Nematic scattering liquid crystal electro-optical elements are well known in the prior art, as described, for example, in U.S. Pat. No. 3,322,485, issued on May 30, 1967, to Williams. Twisted liquid crystal electro-optical elements which require the use of polarizing elements, are also well known in the art, as described, for example, in the aforementioned Fergason '796 patent. The Fergason '796 patent and U.S. Pat. No. 3,834,792, issued on Sept. 10, 1976, to Janning, describe two arrangements for aligning liquid crystal molecules in a display in order that polarized light passing through the material in the absence of an electric field is rotated. The Fergason '796 patent teaches rubbing each of the glass plates which enclose the liquid crystal material in a single predetermined direction and thereafter positioning the plates with the directions of rubbing of the plates forming an angle through which the polarized light is to be rotated. The Janning '792 patent teaches the growth of an alignment film on each plate and then the arranging of the plates with the directions of growth on each of the plates forming a desired angle with respect to one another. Both the Fergason '796 and the Janning '792 patents disclose arrangements of polarizers and twisted liquid crystal cells.
U.S. Pat. No. 3,820,875, issued on June 28, 1974, to William Bohmer, the applicant herein, discloses devices utilizing field-effect scattering dielectrics, such as for example, nematic liquid crystal materials and mixtures of cholesteric and nematic liquid crystal materials. The '875 patent also discloses scanning devices incorporating such dielectrics. The disclosure of the '875 patent is incorporated herein by reference.
U.S. Pat. No. 3,807,831 issued on April 30, 1974 to Soref discloses a liquid crystal display device which includes interleaved arrays of alternate parallel electrodes. A field is induced between interleaved electrodes.
Optoceramic devices are disclosed in C. E. Land, P. D. Thatcher and G. H. Haertling, Electro-optic Ceramics, Academic Press, 1974 at pages 137-233.
Liquid crystals and liquid crystal displays are described in 14 R. Kirk & D. Othmer, Encyclopedia of Chemical Technology 395-427 (3rd ed 1981) and 7 R. Kirk & D. Othmer, supra, at 726-33 (3rd ed. 1979), the teachings of which are incorporated by reference. Liquid crystal displays are commonly used in calculators and digital watches, and thin screen television displays are being introduced.